Artificial limbs have been in use throughout history, having been first recorded circa 2750 B.C. During that period of time, interfacing and suspending an artificial limb has been a continuing challenge. Various and numerous theories and anatomical constructs have been used over time in an evolving manner, and these have revealed a number of key factors in maximizing comfort and functional potential for persons who wear artificial limbs.
Firstly, the surgical procedure used to perform limb amputation is an important factor. The size and shaping of the patient's residual limb is often important to the comfort the patient will later have with a prosthesis. Stated simply, it is critical that the residual limb and prosthesis interface tightly and couple and distribute pressure evenly across the surface of the residual limb.
Early versions of artificial limbs required the use of leather or equivalent straps or belts to suspend the artificial limb upon the person. Later systems employed linkage techniques such as condylar wedges, rubber or synthetic elastic tubing, thermoplastic roll-on sleeves with pin locking systems, and sub atmospheric pressure. Of these, sub atmospheric pressure is typically preferred, because it creates a linkage that provides maximum proprioceptive feedback and control for the artificial limb user. It also provides the best linkage between the user's limb and the prosthetic device.
Creating a reliable sub atmospheric pressure chamber between the residual limb and prosthetic device has, however, proved to be a challenge. As new airtight thermoplastic and thermo set materials have evolved, along with airtight thermoplastic roll-on liners, the potential for creating a sub atmospheric pressure within the prosthetic chamber has improved. Specifically, the patient's residual limb is covered with a roll-on urethane or other thermoplastic liner, which helps to protect the user's tissue from unwanted isolated high negative pressure values, and provides cushioning for the tissue at the same time. The liner also helps to distribute the sub atmospheric pressure applied to the user's limb in a more uniform manner.
Several means for creating an elevated negative pressure chamber within the artificial limb interface have emerged. One method disclosed in U.S. Pat. No. 6,554,868, utilizes a weight activated pump, in which sub atmospheric pressure is maintained strategically within the artificial limb interface cavity as the user walks. This approach has the advantage of continuing maintenance of vacuum as the patient ambulated with the artificial limb. However, the problem with this method is that the pump is heavy, and cannot be removed even in the case of a pump failure. Furthermore, the pump requires a certain minimum space between the user's limb and prosthetic foot, which may be more than is available if the patient has a relatively long residual limb. This prohibits the use of this technology for many artificial limb users. Another disadvantage of this system is that it requires a number of weight activated strokes before the sub atmospheric pressure pump linkage system becomes effective.
Another method disclosed in the above-referenced patent uses a hand-held sub atmospheric pressure pump, much like that used to bleed brake systems on an automobile. This method works well, but requires the individual to carry the hand-held pump upon their person to use in case of vacuum failure. It is also awkward to use for many individuals and requires a certain amount of dexterity and strength to operate. This is a common problem for elderly individuals.
Thus, there is a need for improved technology for achieving sub atmospheric pressure within an artificial limb chamber.